Rail vehicles, such as a train having one or more locomotives, for example, travel along a route from one location to another. Some trains travel along the route in an automatic mode, in which, prior to traveling along the route, a controller predetermines one or more train parameters, such as speed and notch setting, for example, at each location along the route. In order to predetermine the train parameter(s) at each location along the route, the controller may use a memory which prestores a characteristic of the route at each location, such as the grade, for example. While traveling along the route, it is important for the controller to be aware of the train location, to ensure that the actual train parameter(s) track the predetermined train parameter(s), at each train location. Additionally, since the route may include various train parameter restrictions, such as a speed restriction, for example, the controller needs to be aware when the train location is approaching a train parameter restriction location, so to adjust the train parameter(s), if needed, to comply with the train parameter restriction.
Alternatively, the train may travel along the route in a manual mode, in which the train operator is responsible for manually adjusting the train parameter(s). As with the automatic mode, while traveling along the route, it is important for the train operator to be aware of the train location, such as when the train location approaches a train parameter restriction location, for example. The train operator would then manually adjust the train parameter(s) to comply with a train parameter restriction.
Conventional systems have been designed to assist the controllers in the automatic mode and the train operators in the manual mode, to provide a location of the train, as the train travels along the route. However, these conventional systems rely solely on a global positioning satellite (GPS) system, which provides one measurement of the train location, based on satellite positioning or other positioning systems using wireless network or wayside equipment, for example. Upon receiving the positioning system measurement, the controller typically uses its memory to convert this raw position measurement to a distance measurement along the route.
As with any measurement system, the position measurement system is capable of error, such as if the GPS receiver of the train fails to communicate with a sufficient number of satellites, or an error in the memory of the controller which may convert an accurate raw GPS measurement to an inaccurate distance measurement along the route, for example. Accordingly, it would be advantageous to provide an independent distance measurement in addition to the GPS measurement along the route, so to ensure that the distance estimation provided to the controller or train operator is somewhat reliable. Additionally, it would be advantageous to assign a quality value to the distance estimation provided to the controller or train operator.